Implantable electronic medical devices represent a large and growing commercial market. The lifetime of implanted electronic medical devices is typically limited by the life of their primary (non-rechargeable) batteries. Replacing them requires a costly procedure to remove the previously implanted medical device and replace it with another that contains new primary batteries. The surgery also introduces the risk of infection.
Rechargeable batteries carry the promise of a longer overall lifetime for many applications, reducing the number of such procedures, hence the costs in money and trauma to the patient. The lifetime of a permanent implanted battery, perhaps 7-10 years, may be adequate for some applications. But in pain neurostimulators and combination pacemakers-defibrillators, the batteries are discharged faster, sometimes depleting their batteries in 1-3 years. Moreover, children and young adults who get these implants will face many more permanent battery replacements, so even incremental increases in implant lifetime will be useful.
U.S. Pat. No. 8,082,041 (Radziemski) (incorporated herein by reference) describes an ultrasound system suitable for providing power to implanted devices such as pacemakers, defibrillators, and neurostimulators, and sensors primarily to recharge implanted batteries, however with the capability of also delivering power directly to an application. Batteries for such low power devices may be charged for periods of minutes to hours at rates that vary from once per day to once per week or month, or even less frequently. The aforesaid patent also contains a description of medical ultrasound power transmission.
Several methods for providing data for alignment of transmitter and receiver are taught in Radziemski. Typically, in those prior systems the alignment would be performed manually, by physically adjusting the orientation of the external transmitter unit in response to the data provided.
U.S. Pat. No. 8,974,366 (Radziemski and Makin) (incorporated herein by reference), discloses a full-time energy delivery ultrasound method to a storage device or directly to an application, plus a full-time non-mechanical alignment system.
Willis (US2008/0294208), incorporated herein by reference, teaches a two-dimensional ultrasound array to scan and search for a receiver located in or on the heart, to wirelessly provide pacing level voltages to the heart. Willis (U.S. Pat. No. 8,364,276), incorporated herein by reference, estimates the energy per pacing pulse provided as 0.17 micro Joules in a 0.5 millisecond pulse. Assuming a pulse rate of 60 per second, this converts to an average power of 0.17 micro Watts.